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New research suggests that there could be health hazards associatedwith consuming excessive amounts of beta-carotene. This antioxidant is a naturally occurring pigment that gives colorto foods such as carrots, sweet potatoes and certain greens. Italso converts to vitamin A, and foods and supplements are the onlysources for this essential nutrient. But scientists at Ohio State University have found that certainmolecules that derive from beta-carotene have an opposite effect inthe body: They actually block some actions of vitamin A, which iscritical to human vision, bone and skin health, metabolism andimmune function. Because these molecules derive from beta-carotene, researcherspredict that a large amount of this antioxidant is accompanied by alarger amount of these anti-vitamin-A molecules, as well. Vitamin A provides its health benefits by activating hundreds ofgenes. This means that if compounds contained in a typical sourceof the vitamin are actually lowering its activity instead ofpromoting its benefits, too much beta-carotene could paradoxicallyresult in too little vitamin A. The findings also might explain why, in a decades-old clinicaltrial, more people who were heavily supplemented with beta-caroteneended up with lung cancer than did research participants who took no beta-carotene at all.The trial was ended early because of that unexpected outcome. The scientists aren't recommending against eating foods high inbeta-carotene, and they are continuing their studies to determinewhat environmental and biological conditions are most likely tolead to these molecules' production. "We determined that these compounds are in foods, they're presentunder normal circumstances, and they're pretty routinely found inblood in humans, and therefore they may represent a dark side ofbeta-carotene," said Earl Harrison, Dean's Distinguished Professorof Human Nutrition at Ohio State and lead author of the study."These materials definitely have anti-vitamin-A properties, andthey could basically disrupt or at least affect the whole bodymetabolism and action of vitamin A. But we have to study themfurther to know for sure." The study is scheduled for publication in the May 4, 2012, issue ofthe Journal of Biological Chemistry. Previous research has already established that when beta-caroteneis metabolized, it is broken in half by an enzyme, which producestwo vitamin A molecules. In this new study, the Ohio State researchers showed that some ofthese molecules are produced when beta-carotene is broken in adifferent place by processes that are not yet fully understood andact to antagonize vitamin A. Harrison is an expert in the study of antioxidants calledcarotenoids, which give certain fruits and vegetables theirdistinctive colors. Carotenoids' antioxidant properties areassociated with protecting cells and regulating cell growth anddeath, all of which play a role in multiple disease processes. For this work, he joined forces with co-authors Robert Curley,professor of medicinal chemistry and pharmacognosy, and StevenSchwartz, professor of food science and technology, both at OhioState. Curley specializes in producing synthetic molecules in thepursuit of drug development, and Schwartz is an expert atcarotenoid analysis. Curley manufactured a series of beta-carotene-derived molecules inthe lab that match those that exist in nature. The researchers thenexposed these molecules to conditions mimicking their metabolismand action in the body. Of the 11 synthetic molecules produced, five appeared to functionas inhibitors of vitamin A action based on how they interacted withreceptors that would normally launch the function of vitamin Amolecules. "The original idea was that maybe these compounds work the wayvitamin A works, by activating what are called retinoic acidreceptors. What we found was they don't activate those receptors.Instead, they inhibit activation of the receptor by retinoic acid,"Curley said. "From a drug point of view, vitamin A would be calledan agonist that activates a particular pathway, and these areantagonists. They compete for the site where the agonist binds, butthey don't activate the site. They inhibit the activation thatwould normally be expected to occur." The compounds also have been found previously in cantaloupe andother orange-fleshed melons, suggesting humans might even absorbthese molecules directly from their diet. Harrison noted that the findings might explain the outcome of awell-known clinical trial that has left scientists puzzled foryears. In that trial, people at high risk for lung cancer - smokersand asbestos workers - were given massive doses of beta-caroteneover a long period of time in an attempt to lower that risk. Thetrial ended early because more supplemented participants developed cancer than did those who received no beta-carotene. This outcome wasreinforced by results of a follow-up animal study. "Those trials are still sending shockwaves 20 years later to thescientific community," said Harrison, also an investigator in OhioState's Comprehensive Cancer Center. "What we found provides aplausible explanation of why larger amounts of beta-carotene mighthave led to unexpected effects in these trials." The research also has implications for efforts to bio-engineerstaple crops in developing countries so they contain excessbeta-carotene, which is considered a sustainable way to providethese populations with pro-vitamin A. Existing projects includeproduction of golden rice in Asia, golden maize in South Americaand cassava in Africa. "A concern is that if you engineer these crops to have unusuallyhigh levels of beta-carotene, they might also have high levels ofthese compounds," Harrison said. The researchers are continuing to study these compounds, includingwhether food processing or specific biological processes affecttheir prevalence. Previous studies have suggested that oxidative stress , which can result from smoking and air pollution exposure, canlead to higher production of these anti-vitamin-A molecules,Harrison noted. Additional References Citations. We are high quality suppliers, our products such as Rfid Reader Writer Manufacturer , Rugged Tablet PCS for oversee buyer. 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